A letter by Roger Casement to the police inspector responsible for his custody, written just three months before his execution and detailing his attitude towards England and the English, is to be auctioned at Sotheby’s in London next month.

Casement wrote the letter – dated May 17th, 1916 – to Joseph Sandercock, an inspector in the London Metropolitan Police with responsibility for counterespionage, days after being committed to stand trial for treason.

In the letter, he quotes Robert Louis Stevenson and compliments Sandercock on his “wholly chivalrous and high minded” manner.

“From the time you took me in custody at Euston on Easter Sunday and again took me to the Tower on Easter Tuesday you showed me the best side of an Englishman’s character – his native good heart,” he wrote.

“Whatever you may think of my attitude towards your Government and the Realm I would only ask you to keep one thing, in that good heart of yours – and that is that a man may fight a country and its policy and yet not hate any individual of that country . . .”

Casement had been arrested a month previously at Banna Strand in Tralee Bay, Co Kerry while attempting to smuggle in German weapons for the Irish Volunteers in advance of the Easter Rising.

His trial and eventual execution marked a spectacular change of fortune for the former British consular official, who had been knighted for exposing atrocities in the rubber industry in Brazil.

The letter is being sold at an auction of literary and historical manuscripts on December 10th, with a guide price of £8,000–£12,000 (€9,400–€14,200).

It is described by Sothebys as “an exceptional letter, deeply revealing of Casement’s complex and chivalrous character, written three months before his execution.”

“This letter is a fine example of the humane character of a man who was transformed by his execution into a martyr and potent symbol of the Irish nationalist cause,” the auction house adds in the notes accompanying the lot.

The letter is understood to have been held by Sandercock’s family descendents until now.

The auction also contains several interesting lots connected with Ireland’s “Liberator” Daniel O’Connell, including as series of affectionate letters written to his wife in 1820s.

The letters, addressed to “my own love” and “my darling heart”, inform her of his progress in the days leading up to his speeches in London against the proposed suppression of the Catholic Association, and have a guide price of £5,000 – £7,000 (€5,900 -€8,200).

Also up for auction is O’Connell’s travelling case or nécessaire, containing shaving implements, scents and other items, which is likely to have accompanied him as he travelled around Ireland speaking at “monster rallies”, guiding at £2,000 – £3,000 (€2,400 -€3,500).